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Chapter 6
Mendelian Genetics
Genetics – the scientific study of heredity
Gregor Mendel is said to be the father of
genetics.
Mendel used pea plants to study the
inheritance of traits.
True-breeding – plants that produce
offspring identical to themselves.
Parents that have different traits will produce
hybrids.
Hybrids are offspring of parents with
different traits.
Traits – Traits are specific characteristics
(like blue eyes or 5 fingers)
Mendel’s Pea Traits
Genes are factors that are passed from one
generation to the next. (From parents to
offspring)
Alleles are different forms of a gene (like
purple or white flowers).
Law of Dominance
This principle states that some alleles are
dominant and others are recessive.
The dominant allele is represented by an
uppercase letter.
P – purple flower
The recessive allele is represented by a
lowercase letter.
p – white flower
Dominant – Trait that will hide or mask the
recessive trait
Recessive – Trait that will show only when
found with another recessive allele
Genotype – what the alleles are
Phenotype – observable characteristics
P Generation is the first parental generation.
F1 is called the first filial generation or the
first offspring when the P generation is
crossed.
F2 is called the second filial generation or
the offspring from crossing the F1
generation.
Mendel’s Law of Segregation
• Mendel wanted to know what happened to
the recessive alleles.
• He allowed for F1 plants to self pollinate
and this resulted in some F2 plants
showing the recessive trait.
• The two alleles separate when organisms
produce gametes, or sex cells. Each
gamete carries a single copy of each
gene.
• Homozygous - Organisms that have two
identical alleles for a particular trait
Ex. TT or tt
• Heterozygous - Organisms that have two
different alleles for a particular trait
(Hybrids) Ex. Tt
Punnett squares show:
• Possible genotypes
• The alleles in the gametes of parents
• All possible results of a genetic cross
Probability
• Probability is the likelihood that a specific
event will occur.
• Flip a coin 100 times; record the number
of times it is heads _____ and tails_____
• Principles of probability can be used to
predict the traits of offspring produced by
genetic crosses
Mendel’s Law of Independent
Assortment
Genes for different traits can segregate (on
separate chromosomes) independently
during the formation of gametes.
Example: Seed shape doesn’t determine
seed color.